Seal assembly with a hard seal layer actuated through a silicone layer

ABSTRACT

A seal assembly includes a body portion of an element to be sealed, a groove formed into the surface of the body portion, a seal member of a relatively hard material for sealing a gap formed between the surface of the body portion and another element to be sealed. The groove has a space defined proximate its bottom for receiving a pressure medium, a protrusion or protrusions extending into the groove between the pressure medium space and the seal member, and a silicone rubber layer, cast in situ between the space and the seal member and around the protrusion, for transferring pressure from the pressure medium to the seal member and for sealing the groove to prevent escaping pressure medium. In accordance with another aspect of the invention, the assembly has substantially the same structure, but an inflatable tube extends into the pressure medium space, and the silicone layer is cast in situ at least partly around the tube. The protrusion need not be provided. A method for forming the seal assemblies includes casting the silicone rubber layer in situ.

This is a continuation of application Ser. No. 08/023,888, filed Feb.26, 1993, which is a continuation-in-part of application Ser. No.07/761,741, filed Sept. 16, 1991, now abandoned.

FIELD OF THE INVENTION

The present invention relates to a seal assembly for packing a gapbetween two surfaces.

SUMMARY OF THE INVENTION

An object of the invention is to provide an actuable seal assembly,particularly a hydraulic-oil or compressed-air or mechanically operatedseal, said seal being capable of withstanding substantial pressures,even pressures of several hundred bars, but being well suitable also forminor pressures. In the context of this application, compressed airrefers not only to air but to any gas or gas mixtures. A seal of theinvention finds a plurality of applications, e.g., in mechanicalcomponents having considerable pressure differences on different sidesof a surface to be sealed, e.g., flap and ball valves, pistons, etc.This type of seal can also be used, e.g., for packing the joints ofunderwater tunnel elements and for sealing of various door and windowstructures, particularly in objects intended for marine conditions andin corresponding structures.

In view of the operation of a seal of the invention, which useselastomers, it is essential that elastomer does not adhere to wallsurfaces, thus allowing the displacement of elastomer in an elastomerspace and/or passages in a pressurized state to a reasonable extent. Thebehavior of elastomer resembles that of a fluid in the sense that it isincompressible, the difference from a fluid being, however, thatelastomer is self-restoring after depressurization. The preliminarytests have indicated that at a pressure of over 200 bars, e.g., in apassage having a diameter of about 5 mm and a length of about 500 mm,there occurs a nearly complete equalization of pressure throughout theentire passage. The nonadherence of elastomer to the walls of passagesor elastomer spaces can be enhanced, e.g., by the application of variouslubricants which are compatible with any given elastomer. The elastomerpassages/spaces must generally be formed larger than corresponding fluidpassages.

If necessary, elastomer can be bonded, e.g., to a sealing layer of someharder material or, when using, e.g., mechanical pistons, to the head ofa piston by the application of an appropriate binder, such as, e.g.,Chemosil X 5201, available from, e.g., Henkel AG (FRG).

The most significant advantage gained by a seal of the invention is thatthe installation work will be facilitated as the seal can be cast ormolded to position in situ in an already assembled device, thus avoidingdamages to the seal. In addition, after the molding operation, the sealcan be pressurized/adjusted to a desired pressure reading.

Another advantage gained by a seal of the invention is a considerablepressure resistance and, depending on selected materials, also aconsiderable heat resistance. Another advantage is that a systemprovided by the seal and its pressurizing medium can be designed as aclosed system, whereby, e.g., possible spills of hydraulic oil can bereliably prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference made to theaccompanying drawings, in which:

FIGS. 1-4C illustrate various respective embodiments of a seal of theinvention, wherein:

FIG. 1 is a sectional view of a first embodiment of a seal assembly fora cylinder within a body;

FIG. 2 is a sectional view of a seal assembly of the invention for twoconcrete elements;

FIG. 3a is a side view of a seal assembly of the invention for a door;

FIG. 3b is a sectional view taken along line III--III of FIG. 3a;

FIGS. 4a-4c show a seal assembly of the invention for combination with aflap valve, wherein:

FIG. 4a is a top plan view of the flap valve,

FIG. 4b is a front view of the valve, and

FIG. 4c is a sectional view of the valve and seal assembly;

FIG. 5 is a sectional view of a pressurizing unit for the hydraulic oilused in a seal of the invention;

FIGS. 6a-6c illustrate various respective embodiments of "mechanical"pressurizing means used in a seal of the invention, wherein:

FIG. 6a is a sectional view of one such pressurizing mechanism,

FIG. 6b is a sectional view of another mechanism including a spring, and

FIG. 6c is a sectional view of another pressurizing mechanism includingmultiple pistons of different sizes;

FIGS. 7a and 7b are sectional views of a combination of a seal of theinvention and a "mechanical" pressurizing means, wherein

FIG. 7a shows the seal and pressurizing means before actuating the seal;and

FIG. 7b shows the seal and pressurizing means after actuating the seal;and

FIG. 8 is a sectional view of a pressurizing device that includes atemperature controlled heater.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates the sealing assembly for a rotatable shaft 1 againsta body or jacket portion 2. In the embodiment of FIG. 1, an elastomerlayer 3a is fitted in a sealing space 3. The edges of walls definingspace 3 are provided with inwardly directed protrusions 4. Theseprotrusions 4 define therebetween a section A which is substantiallynarrower than the rest of the sealing space. The elastomer layer isdirectly molded in situ on either side of the narrower Section A, thusproducing a massive sealing layer. Between the inner surface of sealinglayer 3a and the bottom of sealing space 3 is provided a space 6a forhydraulic fluid 6 or compressed air or elastomer medium includingvulcanized pieces of silicone elastomer or a room-temperaturevulcanizing silicone elastomer cast in situ in space 6a. On top ofsealing layer 3a is preferably mounted a sealing means 5a, made of,e.g., a harder elastomer, for effecting the actual sealing. Sealingmeans 5a is preferably vulcanized to be integral with sealing layer 3a.

Preferred elastomers include various silicones such as two-component,room-temperature vulcanizing silicone rubber. One example is siliconerubber RTV-2, shore hardness approximately 18 to 70, manufactured byWacker-Chemie GmbH, Federal Republic of Germany. Most preferably, theelastomer used is selected from condensation hardener based siliconeelastomers which set at room temperature. An advantage offered bysilicone is that it does not readily stick to metal surfaces and iscapable of deforming by the application of a minor force, behaving inthe same way as a liquid in the sense that it cannot be permanentlycompressed.

It is also preferred that the elastomer be cast in situ. This eliminatesthe need for manufacturing separate molds independently for eachapplication. If the silicone is cast in situ, it is preferred to use atwo-component casting machine with a variable mixing ratio. The in situcast elastomer is kept from substantially adhering to the walls by usingan appropriate release agent such as various lubricants, waxes andpowders that are compatible with the elastomer. For silicone,conventional soap and silicone grease have proved to be suitable releaseagents. During the operation of the sealing device, this type of releaseagent may gradually work its way out of the elastomer space and/orpassages. However, the effect of such ejection of the release agent uponthe adherence of elastomer to the walls remains practically negligibledue to the fact that the reciprocating movement of elastomer relative tothe walls causes a gradual crumbling of elastomer at the interfacebetween the walls and the elastomer. The layer of crumbled elastomeracts as a release layer that prevents elastomer from sticking to thewalls.

The seal, is operated by hydraulic fluid 6 that is pressurized by usinga pressurizing unit 20, such as that described later and shown in FIG.5. The hydraulic fluid applies pressure to elastomer sealing layer 3aresulting in a displacement of the sealing layer outward and, throughthe action of narrow section A, a deformation in sealing layer 3a, aswell as the orientation of forces created in sealing layer 3asubstantially against protrusions 4. This deformation of sealing layer3a produces a pressure effect on the harder sealing means 5a urging itagainst body portion 2 so as to seal or pack a gap 5 between bodyportion 2 and shaft portion. When the pressure exerted by hydraulicfluid subsides, said sealing layer 3a resumes its shape through theaction of a return force produced by the effect of narrow section A.Naturally, in certain cases, the packing or seal can be directlyeffected by means of sealing layer 3a.

The embodiment of FIG. 2 shows an example of the packing of a jointbetween two concrete elements 7, 8. In this embodiment, inside a seal 9there is formed an inflatable space 10 for a pressure medium. This spaceis formed, e.g., in such a manner that seal 9 is directly cast in situaround a nonreinforced two-component elastomer tube, or a prefabricatedseal 9 is provided in a hole extending therethrough with a nonreinforcedtwo-component elastomer tube. Seal 9 is placed or molded in the sealingspaces made in both surfaces to be sealed. The seal can be madepressure-resistant by supplying said space 10 with a pressurizedhydraulic fluid or compressed air or some elastomer medium, whereby thepressurization of hydraulic fluid can be effected, e.g., by means of apressurizing unit 20 shown in FIG. 5.

The embodiments of FIGS. 3a and 3b illustrate the use of a seal of theinvention for sealing a door. In this embodiment, a sealing space 14 ispreferably designed in a dovetail groove in the edge of a door to extendaround the entire periphery of the door. The sealing space is fittedwith a sealing layer 14a by casting it directly in situ around anonreinforced two-component inflatable elastomer tube 13 (e.g., astandard hose), preferably near the bottom of sealing space 14.Pressurization of tube 13 with the application of a hydraulic fluid orsilicone elastomer pieces can be effected by means of a pressurizingunit such as shown in FIG. 5. As pressurized hydraulic fluid is suppliedtherein, tube 13 expands resulting in a deformation in relatively softelastomer layer 14a which, upon its outward expansion/displacement,presses against relatively hard sealing member 14b to seal a gap 12between door 15 and jamb 16.

Expandable and contractible tube 13 contracts upon the release of thepressure therein which causes layer 14a to retract, with help from thedovetail, and the sealing member 14b thus releases its sealing pressure.Preferably, member 14B is fixed to layer 14a so that layer 14a pullsmember 14b inward when layer 14a retracts.

FIGS. 4a-4c illustrate the use of a seal of the invention in a flapvalve. A flap 55 is normally sealed, e.g., by means of a metal gasket 51having a U-shaped cross section. The performance of this gasket can beimproved in accordance with the invention by casting an elastomer layer52 in the groove of metal gasket 51. The casting is preferably effectedaround an elastomer tube 53 fitted in the groove, said tube beingconnected with pressurization means for pressurizing the tube with anappropriate medium, such as hydraulic oil, compressed air or elastomer.On top of elastomer layer 53 is preferably laid a sealing layer 54 whichis made, e.g., of harder elastomer. This solution can also be effected,e.g., in a manner that an elastomer tube 53 fitted in the groove of ametal gasket matches in its cross section substantially the size of saidgroove, the elastomer being only cast inside said tube while the tubeserves as a means carrying said sealing layer 54.

The pressurization of seal assemblies of the invention is preferablyeffected by means of a pressurizing unit 20 shown in FIG. 5. Thepressurizing unit 20 preferably comprises a bushing-like body portion36, fitted with a protrusion 39, fitted with an external threading andextending outward of cavity 26. Protrusion 39 is provided with a holeextending into cavity 26 and preferably fitted with an internal flange41 at the end of protrusion 39 away from cavity 26. The cavity 26 ofbody portion 36 includes a space 28 for hydraulic fluid 7, e.g., bymeans of an elastomeric membrane 21 and a massive elastomer layer 22. Inorder to connect space 28 to a tube 37, the bottom of cavity 26 isprovided with a coupling 27, comprising a connector tube 30 which has aninternal hole and one end of which is provided with an expansion 31 andthe other end with a threaded portion 32, the internal throughhole 30aextending through expansion 31 and threaded portion 32. The couplingfurther includes a separate "bead" portion 33 and a separate sleeveportion 34. The coupling 27 is assembled in a manner that the bottom ofmembrane 21 carries a tubing section 35 which is pushed on top of theconnector tube expansion 31 to extend beyond said expansion in thelongitudinal direction. This is followed by placing the bead portion 33on top of connector tube 30 from the end facing said threaded portion 32and pushing it on top of tubing section 35 into the abutment withexpansion 31. The bead portion 33 is preferably designed to includeinternal cones at both ends thereof. This is then followed by placingsaid sleeve portion 34 on top of connector tube 30 from the threaded end32 and pushing it against bead portion 33 in a manner that said tubingsection 35 is retained between bead 33 and sleeve 34. Finally, saidconnector tube 30 is fastened to body portion 36 by means of a nut 38 tobe fastened to said threaded portion 32 extending through the hole ofprotrusion 39, said nut being tightened to a suitable tightness. Theelastomer layer 22 surrounds membrane 21 completely up to coupling 27.

The section between layer 22 and the outer surface of body portion 36further includes a piston 23 and between piston 23 and layer 22 there isalso a gasket 25, made, e.g., of teflon or copper. In addition, the unit20 preferably includes a plunger 24 which extends through piston 23 andgasket 25 into elastomer layer 22. The inner end of plunger 24 isprovided with an enlargement 24a for improved adherence to layer 22. Themovement of piston 23 and plunger 24 is effected, e.g., by means ofconventional hydraulic, pneumatic or mechanical equipment. The space 28can also be formed in a manner that the coupling member 27 is mounted onbody portion 36 without any separate membrane 21 and its tubing section.This is followed by placing in cavity 26 an element made of, e.g.,stearine or a similar material, which serves as a mold for space 28.This is followed by casting an elastomer layer 22 in the cavity and thislayer is kept under pressure until it is solidified. Being underpressure, the elastomer penetrates into a gap between the conicalsurfaces of bead portion 33 and sleeve portion 34 setting in itsposition. After the elastomer is set, the stearine block formed in space28 is melted by heating for draining the stearine out along the internalhole of connector tube 30. Finally, the pressurizing unit is attached toa cavity built, e.g., in a separate body element 42, the bottom of saidcavity being provided with a threaded hole for protrusion 39, wherebysaid threaded hole can be sealed in a conventional manner, e.g., bymeans of a teflon strip. The bottom of the threaded hole in the cavityof body element 42 is further provided with a hydraulic tube 37 whichcan be further connected to a tube internal of the sealing, e.g., bymeans of the above-described coupling 27. This arrangement is capable ofproviding a closed assembly in a manner that the hydraulic oil in thesystem is contained in a passage confined at any given time by massiveelastomer layers and thus, in practice, there are no holes for spills tooccur.

FIGS. 6a-6c illustrate some embodiments for mechanical pressurizingelements used in seal assemblies of the invention. On the one hand, apressurizing element, such as a piston, a rod or the like, produces apressure effect directly in the elastomer or elastomer medium whichmakes up a sealing layer. On the other hand, the elastomer medium canjoin directly with said sealing layer or through the intermediary ofhydraulic oil, whereby the system can be referred to ashydro-mechanical, thus corresponding in principle to the hydraulic oilpressurizing unit shown in FIG. 5.

In the embodiment shown in FIG. 6a, a pressuring element 61 comprises anouter piston member 68 provided with a threaded portion 62 and havinginside it an inner piston 64. The inner piston 64 is operated, e.g., bymeans of a screw member 66, said screw member being connected to outerpiston 68 with a threading 63 through a spacer block 65. The screwmember 66 is further provided with an operating head 67. The innerpiston can also be operated, e.g., by means of an eccentric or someother per se known mechanical element. The outer piston member 68 isused for fixing the pressure medium 61, e.g., to the body section of apiece to be sealed, and it also serves as an initial pressure adjuster.The inner piston 64 performs the actual pressurization. The frontsurface of outer piston 68 facing the elastomer space or medium ispreferably provided with a groove 69, the inner edge of outer piston 68being formed with a lip portion 70 for preventing the passage ofelastomer between inner piston 64 and the internal surface of outerpiston 68 as said inner piston 64 extends beyond said front surface ofouter piston 68. The inner piston 64 is provided with a correspondinglip portion 61 for preventing the passage of elastomer between inner andouter pistons as said piston 64 is positioned inside outer piston 68. Atits end facing the elastomer, said inner piston 64 can be designed,e.g., wedge-shaped, for a more uniform distribution of the pressureapplied to elastomer.

FIG. 6b illustrates a pressure medium similar to that of FIG. 6a, butfitted with a spring 72 which compensates for variations in thevolume/pressure of elastomer caused by variations of temperature. Thistype of volume/pressure control can also be achieved by controlling thetemperature, e.g., by means of electric resistance or the like.

Silicone rubbers such as are used with this invention generally exhibitvery high thermal expansion, on the order of 6-8% per 100° C. A 6%compression of silicone rubber can cause a pressure increase of 1000bar. It is desirable to include temperature controlling means tocompensate for pressure changes caused by deviations in temperature.

Such a pressurizing device that includes a temperature-controlledheating element is illustrated in FIG. 8. Elastomeric sealing layer 3ain sealing space 3 includes electric heating coil 90 andtemperature-controlled heating element 95. As heat is applied to thesealing layer, the elastomer expands causing an increase in pressurewhich effects the seal. As heat is removed, the elastomer contracts,reversing the seal. The elastomer is preferably cast in situ around theheating coil within the sealing space.

FIG. 6c illustrates an embodiment comprising a plurality of differentsize pistons connected successively to each other. For example, a screwthread is used for providing a body section 100 with a spacer block 101,fitted with a first piston or rod 102. The first piston acts on a firstelastomer layer 103 which transmits the pressure to a second piston 104,having a surface area substantially larger than that of said firstpiston 102. The surface of second piston 104 facing away from firstelastomer layer 103 is provided with a third piston 105, having asurface area substantially smaller than that of said second piston 104.The third piston 105 produces an increased pressure on a secondelastomer layer 106 inside an inner tube 107, said piston assemblyserving as an pressure booster or amplifier. The direction ofamplification depends on the ratio of the piston surface areas to eachother. In the embodiment shown in FIG. 1, for example, a secondelastomer layer 106 is included in elastomer space 3 for pressurizing asealing layer 3a therein. In this case, the elastomer layer 106 ispreferably made of the same elastomer as sealing layer 3a and cast as anintegral compound.

FIGS. 7a and 7b illustrate a combination of a mechanical pressurizingmechanism and a seal assembly. FIG. 7a shows the combination in aninitial nonsealing position and FIG. 7b in an activated sealingposition. The closed system shown in FIGS. 7a and 7b includes thepressurizing mechanism and the seal assembly which are connected by aconduit 6a formed within a body section 80. The body section ispreferably formed by two elongate components mounted together with theinterface plane extending in an axial direction. The pressurizingmechanism includes a cylinder 86 threaded to the body section 80. Insidethe cylinder 86 there is a piston 83 provided with a threaded controlportion 84 which allows adjustment of piston 83. The cylinder 86communicates with a tapered first space 87 filled with elastomer 87awithin the body, the walls of space 87 being treated with a suitablelubricant for allowing the elastomer 87a to move freely in space 87,thereby providing for transmission of pressure. The end of piston 83abuts the elastomer 87a and is provided with a gasket 88 for preventingpassage of elastomer into a gap between piston 83 and cylinder 86 orinto a gap between cylinder 86 and body section 80. The elastomer 87within the first elastomer filled space communicates with sealing space3 by conduit 6a. The sealing assembly comprises an elastomer sealinglayer 3a as well as a sealing member 5a of a harder elastomeric materialrelative to the sealing layer 3a.

The sealing layer 3a and sealing member 5a together fill a groove 6bthat is defined by a surface of the body section. The inner portion ofthe groove includes side walls with protrusions 3b. Elastomer ispreferably cast in situ in this inner groove portion to form elastomericsealing layer 3a. It is also preferred that this elastomeric sealinglayer 3a be bonded to the sealing member 5a.

To assemble the structure shown in FIGS. 7a and 7b, e.g., sealing member5a is placed in position between the halves of body section 80, followedby joining the body section halves together, e.g., by means of a screwconnection (not shown). This is followed by fitting cylinder 86 in itsposition and by carrying out elastomer casting with the help of piston84 for laying the elastomer in its location. The first elastomer 87a inspace 87a, conduit 6a and elastomeric sealing layer 3a can be cast as asingle element, or sealing layer 3a can be cast separately, e.g., byproviding separate casting gates leading into sealing space 3 and byblocking passage 6a, e.g., with a wax plug that can be removed after thesealing layer is set. The wax plug can be removed, e.g., by vaporizationor by using appropriate chemicals.

The pressure from piston 83 is transmitted to sealing layer 3a by meansof elastomer 87a, which extends from layer 3a to gasket 88.Alternatively, elastomer 87a may comprise a two-componentroom-temperature vulcanizing silicone in pieces. Thepressure-transmitting medium can also comprise a hydraulic oil inconduit 6a (such as hydraulic fluid 6 in FIG. 1), whereby the sealinglayer is cast first, the wax plug is removed, conduit 6a is filled withoil and an elastomer layer is cast in first space 87 to keep the conduit6a with hydraulic oil closed by elastomer on each side of the oil. Sucha closed system eliminates the possibilities of a hydraulic fluid leak.

Such a sealing assembly has a variety of applications, e.g., in flap andball valves, and pistons. In such applications, temperature differencescause thermal expansion of the sealing material and must be compensatedto achieve an even seal pressure. This is especially necessary when sealpressure and the pressure of the material to be sealed are close inorder to achieve a low friction seal surface.

The sealing assembly can naturally be different from those describedabove. For example, in the case shown in FIG. 1, the seal can be fittedin jacket member 2 instead of shaft 1.

In operating the sealing member, piston 83 is threaded into the body 80such as by using a suitable tool (not shown) that cooperates with head85 of the threaded portion 84 of the piston. The first elastomer 87a iselastically deformed by the pressure imposed by piston 83 and thispressure is transmitted to the pressure medium in conduit 6a which inturn, transmits pressure to elastomeric sealing layer 3a. The elastomeris elastically deformed by the pressure and driven outwardly from thegroove 6a pressing sealing member 5a outwardly from the surface of body80 to seal against the opposing surface to be sealed 81.

The seal assembly is disengaged by threading piston 83 away from body 80to release the pressure. The protrusions in the lower portion of thesealing space 3a cause the elastomeric sealing layer to spring back toits original shape when the pressure is released. This withdraws sealingmember 5a from engagement with opposing surface 81.

The walls of the groove or cavity are preferably provided with asuitable release agent to minimize friction on layers 3a and 87 to avoidsticking.

The pressurization of seal assemblies of the invention can also beeffected, e.g., by supplying into a space in the conduit or in thegroove some pressurized two-component material which is allowed to setwhile maintained under pressure. Thus, the sealing can be maintained inactivated state for a permanent sealing effect.

What is claimed is:
 1. A seal assembly comprising:a body portion; agroove formed in a surface of the body portion and having inner andouter portions, wherein the outer portion includes first side walls andthe inner portion includes second side walls, and a bottom wall; a sealmember disposed in the outer portion of the groove and in slidableengagement with the first side walls for sealing a gap between thesurface of the body portion and a cooperating surface of an element tobe sealed; an inflatable tube in the inner portion of the groove andfiled with a pressurizing medium; an elastomeric medium surrounding theinflatable tube disposed in the inner portion of the groove, theelastomeric medium being of a softer material than the seal member; anda pressurizing element for releasably applying pressure to thepressurizing medium, wherein the pressurizing means comprises atemperature-controlled heater.
 2. The seal assembly of claim 1, whereinthe elastomeric medium comprises a room-temperature vulcanizing siliconeelastomer compound which is cast in situ in the inner portion of thegroove.
 3. The seal assembly of claim 1, wherein the pressurizing mediumcomprises silicone.
 4. The seal assembly of claim 1, wherein thepressurizing medium is a room-temperature vulcanizing silicone elastomercompound which is cast in situ in the inflatable tube.
 5. The sealassembly of claim 1, further comprising means for compensating forpressure variations in the seal assembly caused by temperature changes.